Tire pressure monitoring system

Abstract

A wireless tire pressure monitoring system warns a driver of a vehicle of low pressure in one or more of its tires so that the driver may take corrective action before a tire blowout occurs. A pressure transducer, transmitter and antenna are integrally housed and mounted to the tire stem of a tire. When the pressure transducer senses a tire pressure below a preselected pressure, the transmitter broadcasts a radio frequency (RF) signal that, upon detection by a receiver mounted on the vehicle, warns the driver of abnormally low pressure. In a preferred embodiment, the transmitter is a SAW device that is periodically interrogated by an RF signal from a transmitter on the vehicle.

What is claimed is: 
     
       1. A wireless monitoring system for indicating the occurrence of a predefined condition with a transducer to which wires and other physical connections cannot be easily made, the monitoring system comprising: transducer means mounted for sensing an occurrence of a predefined condition;   a surface acoustical wave (SAW) device mounted with the transducer means for receiving an interrogating radio frequency (RF) signal that energizes the SAW device for transmitting a predetermined RF echo signal on an antenna in response to the interrogating signal; and   antenna disconnect means coupled between the transducer means and the SAW device for enabling transmitting of the echo signal when the transducer means senses the predefined condition and for disenabling transmitting of the echo signal when the transducer means does not sense the predefined condition.   
     
     
       2. The wireless monitoring system of claim 1 further comprising: transmitter means remotely located from the transducer means and the SAW device for transmitting the interrogating RF signal for receipt by the SAW device;   receiver means remotely located from the transducer means and the SAW device for detecting the echo signal from the SAW device; and   means for warning of the occurrence of the predefined condition, the receiver means coupled for delivering a signal indicating detection of an echo signal to the means for warning.   
     
     
       3. The monitoring system of claim 1 wherein the transducer means and the SAW device are integrally formed. 
     
     
       4. The monitoring system of claim 1 wherein the transducer means and the SAW device are mounted to a rotating object. 
     
     
       5. The monitoring system of claim 4 wherein the transducer means and the SAW device are integrally mounted to a stem of a tire for monitoring the occurrence of air pressure within the tire falling below a predetermined level. 
     
     
       6. The monitoring system of claim 5 wherein the transducer includes a pressure diaphragm operating a switch. 
     
     
       7. The monitoring system of claim 1 wherein the antenna disconnect means is comprised of a switch operated by the transducer means that grounds a transmitting antenna with which the SAW device transmits. 
     
     
       8. A tire pressure monitoring system that warns its driver of a tire having air pressure below a predetermined level, the monitoring system comprising: a pressure sensor for sensing a pneumatic pressure of a vehicles tire;   a SAW device for receiving an interrogating radio frequency (RF) signal and broadcasting a responding RF signal indicative of a pressure sensed, the pressure sensor being coupled to the SAW device for receiving pressure information;   an enclosure for integrally housing the pressure sensor and the SAW device, the housing including means for securing the housing onto a Shrader value of a tire stem and communicating pressure of air within the tire to the pressure sensor and an antenna;   a signal monitoring device for mounting within a vehicle, the signal monitoring device including a transmitter for emitting the interrogating signal and a receiver for detecting a responding signal broadcast from the SAW device; and   means for alerting the driver when the responding signal indicates the sensed pneumatic pressure of the tire is below the predetermined value.   
     
     
       9. The tire monitoring system of claim 8 wherein the transmitter emits the interrogating signal during a transmit interval and the receiver listens for the responding signal during a listen interval that follows the transmit interval, the transmit and listen intervals occurring periodically. 
     
     
       10. The tire monitoring system of claim 8 further comprising: a plurality of enclosures, each one of the plurality of enclosures housing a pressure sensor and a SAW device and mounted onto a Shrader value associated with each of a plurality of tires on the vehicle;   a plurality of antennas, at least one antenna of the plurality of antennas being mounted in each wheel housing having a tire to which one of the plurality of enclosures is secured, the antennas being coupled to the signal monitoring device.   
     
     
       11. The tire pressure monitoring system of claim 10 wherein, each one of the plurality of antennas broadcasts the interrogating RF signal and receives the responding RF signal.